1. Field of the Invention
The present invention relates to a catalyst composition for living free radical polymerization, and more particularly to a process for preparing a polymer with narrow polydispersity using the catalyst composition.
2. Description of the Prior Art
Radical polymerization is one of the polymerization processes which are most widely exploited industrially because of the variety of the polymerizable monomers (50% of the commercial monomers), of the ease of application and of the synthesis processes employed (emulsion, suspension, bulk, solution). However, in conventional radical polymerization it is difficult to control the size of the polymer chains and the molecular mass distribution. The polymers thus prepared contain chains of very large and very small masses (broad polydispersity), and this results in materials with uncontrolled properties. In addition, the sequential addition of monomer produces a mixture of homopolymers.
Anionic and cationic polymerization techniques, for their part, allow proper control of the process, but the reaction conditions required are not always capable of being implemented on an industrial scale. In addition, many monomers cannot be polymerized using these techniques.
Matyjaszewski in U.S. Pat. No. 5,763,548 mainly uses a CuCl/bipyridine catalyst system to effectively control the free radical polymerization of a monomer such as styrene, acylates, methyl methacrylate (MMA) in the presence of an alkyl halide initiator. However, this system suffers from that a large amount of catalyst must be used and the activity is not high enough. Therefore, there is a need to develop a catalyst system with high activity.
An object of the present invention is to solve the above-mentioned problems and to provide a catalyst composition that can be used to synthesize polymers through living free radical polymerization with high activity. There is no need to isolate the catalyst composition, and in the presence of a suitable initiator, the catalyst composition can be directly reacted with a monomer in situ, that is, directly reacted with a monomer in the state when each component is mixing.
Another object of the present invention is to provide a process for preparing polymers through living free radical polymerization using the catalyst composition of the present invention. The polymer obtained has narrow polydispersity.
To achieve the above objects, the catalyst composition for living free radical polymerization of the present invention includes a transition metal complex MXp and a ligand.
In the transition metal complex MXp, M is a transition metal, X is halogen, xe2x80x94NO2, xe2x80x94NCS, xe2x80x94NCO, xe2x80x94SCN, xe2x80x94CN, xe2x80x94N3, xe2x80x94SO4, carboxylate group, or xe2x80x94PF6, p is the valence of the transition metal.
The ligand is represented by formula (I): 
wherein R1 can be the same or different and is C1-20 alkyl, C6-20 aryl, C7-20 alkylaryl, C7-20 arylalkyl, or heterocyclic groups; R2 can be the same or different and is H, C1-20 alkyl, C6-20 aryl, C7-20 alkylaryl, C7-20 arylalkyl, heterocyclic groups, alkyl sulfide groups, nitrile groups, alkylsilyl, or ester groups; n is an integer of 0 to 6; and A is deleted or an S or O atom.
The molar ratio of the transition metal complex MXp and the ligand is 1 to 4.
The process for preparing polymers through living free radical polymerization of the present invention involves contacting a monomer and a catalytically effective amount of the above-mentioned catalyst composition with a compound capable of generating free radicals to undergo homopolymerization or copolymerization. Suitable monomer can be a (meth)acrylic, vinyl, vinylidene, diene, or mixtures thereof.